Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.6.1.3 (ATPase)
 65,361 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

A Na+/H+ antiporter catalyses coupled Na+ extrusion and H+ uptake across the membranes of extremely alkalophilic bacilli. This exchange is electrogenic, with H+ translocated inward greater than Na+ extruded. It is energized by the delta chi 2 component of the delta mu H+ that is established during primary proton pumping by the alkalophile respiratory chain complexes. These complexes abound in the membranes of extreme alkalophiles. Combined activity of the respiratory chain, the antiporter, and solute transport systems that are coupled to Na+ re-entry, allow the alkalophiles to maintain a cytoplasmic pH that is several pH units more acidic than optimal external pH values for growth. There is no compelling evidence for a specific and necessary role for any ion other than sodium in pH homeostasis, and although there is very high cytoplasmic buffering capacity in the alkaline range, active mechanisms for pH homeostasis are crucial. Energization of the antiporter as well as the proton translocating F1F0-ATPase that catalyses ATP synthesis in the extreme alkalophiles must accommodate the problem of the low net delta mu H+ and the very low concentrations of protons, per se, in the external medium. This problem is by-passed by other bioenergetic work functions, such as solute uptake or motility, that utilize sodium ions for energy-coupling in the place of protons.
 ...
PMID:pH homeostasis and bioenergetic work in alkalophiles. 216 8

The F1F0-ATP synthase from the alkaliphilic Bacillus firmus OF4 was purified in a reconstitutively active form, in good yield and with a high specific ATPase activity when appropriately activated. The purification procedure involved octyl glucoside extraction of washed membrane vesicles in the presence of 20% glycerol and asolectin followed by ammonium sulfate fractionation and sucrose density gradient centrifugation. The purified preparation was resolved into seven bands by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, corresponding to the five F1 subunits, alpha, beta, gamma, delta, and epsilon, and to the b and c subunits of the F0. Two-dimensional sodium dodecyl sulfate-poly-acrylamide gel analysis revealed a candidate for the alpha subunit of F0. The MgATPase activity of B. firmus OF4 F1F0 was barely detectable but could be stimulated, optimally more than 100-fold, by sulfite, methanol, and octyl thioglucoside. The enzyme was inhibited by N,N'-dicyclohexylcarbodiimide and sodium azide, but not by aurovertin, an inhibitor of the F1 from Escherichia coli. The F1F0 reconstituted into proteoliposomes catalyzed ATPase activity, ATP-Pi exchange, and ATP-dependent delta pH and delta psi formation. ATP hydrolysis was stimulated by protonophores while the other activities were abolished by protonophores. These activities were neither dependent on added sodium ions nor significantly affected by them. F1F0 proteoliposomes made from crude octyl glucoside extracts that also contained the Na+/H+ antiporter were shown to catalyze ATP-dependent Na+ uptake that was completely sensitive to carbonyl cyanide m-chlorophenyl-hydrazone; Na+ uptake activity was absent in proteoliposomes containing more purified F1F0 but lacking the Na+/H+ antiporter. These data show that the F1F0 translocates protons and does not substitute Na+ for H+ in energy coupling.
 ...
PMID:Purification and reconstitution of the F1F0-ATP synthase from alkaliphilic Bacillus firmus OF4. Evidence that the enzyme translocates H+ but not Na+. 217 11

The fluorescent anionic dye, bisoxonol, and flow cytometry have been used to monitor changes in the membrane potential of rat thymocytes exposed to the B subunit of cholera toxin. The B subunit induced a rapid hyperpolarization, which was due to activation of a Ca2+-sensitive K+ channel. Reduction of extracellular Ca2+ to less than 1 microM by the addition of [ethylene-bis(oxyethylenenitrilo)]tetraacetic acid immediately abolished the hyperpolarization caused by the B subunit. Cells treated with quinine and tetraethylammonium lost their ability to respond to the B subunit, whereas 4-aminopyridine did not have any effect. Thus, calcium-sensitive and not voltage-gated K+ channels appeared to be responsible for the hyperpolarization. The results of ion substitution experiments indicated that extracellular Na+ was not essential for changes in membrane potential. Further studies with ouabain, amiloride and furosemide demonstrated that electrogenic Na+/K+ ATPase, Na+/H+ antiporter and Na+/K+/Cl- cotransporter, respectively, were not involved in the hyperpolarization process induced by the B subunit. Thus, crosslinking of several molecules of ganglioside GM1 on the cell surface of rat thymocytes by the pentavalent B subunit of cholera toxin modulated plasma membrane permeability to K+ by triggering the opening of Ca2+-sensitive K+ channels. A role for gangliosides in regulating ion permeability would have important implications for the function of gangliosides in various cellular phenomena.
 ...
PMID:Interaction of the B subunit of cholera toxin with endogenous ganglioside GM1 causes changes in membrane potential of rat thymocytes. 276 35

The binding of interleukin 2 (IL 2) to specific cell surface receptors provides a unique proliferative stimulus to sensitive T-lymphocytes. The purpose of this investigation was to examine the hypothesis that IL 2 stimulus-response coupling in the IL 2-dependent murine T-lymphocyte clone CTLL-2 employed some of the intracellular second messengers used by other growth factors. No evidence was obtained to implicate changes in intracellular Ca2+ concentrations, protein kinase C activation, or stimulation of the Na+/H+ antiporter or the Na+/K+ ATPase as requirements for stimulation by recombinant human IL 2. Pertussis toxin did not inhibit IL 2-driven growth of CTLL-2, and while cholera toxin did inhibit growth, its effect was optimal 6 to 8 hr after addition of IL 2 and could be mimicked by increased intracellular cyclic-AMP. Thus, guanine nucleotide-binding regulatory proteins do not appear to be involved in stimulation by this lymphokine. Together, these data suggest that IL 2 may not use any of the same types of intracellular second messengers generated subsequent to the binding of antigen or mitogen by T-lymphocytes.
 ...
PMID:Does interleukin 2 stimulus-response coupling result in generation of intracellular second messengers? 284 44

Methanogenesis from formaldehyde or formaldehyde + H2, as carried out by Methanosarcina barkeri, was strictly dependent on sodium ions whereas methane formation from methanol + H2 or methanol + formaldehyde was Na+-independent. This indicates that the reduction of formaldehyde to the formal redox level of methanol exhibits a Na+ requirement. During methanogenesis from formaldehyde, a delta pNa in the range of -62 mV to -80 mV was generated by means of a primary, electron-transport-driven sodium pump. This could be concluded from the following results obtained on cell suspensions of M. barkeri. 1. The addition of proton conductors or inhibitors of the Na+/H+ antiporter had no effect on sodium extrusion. 2. During methanogenesis from formaldehyde + H2 a delta psi of -60 mV to -70 mV was generated even in the presence of proton conductors. 3. ATPase inhibitors, applied in the presence of proton conductors, had no effect on primary sodium extrusion or generation of a delta psi. Evidence for a Na+-translocating ATPase could not be obtained.
 ...
PMID:Electron-transport-driven sodium extrusion during methanogenesis from formaldehyde and molecular hydrogen by Methanosarcina barkeri. 285 Jan 82

The two mitochondrial Na+/H+ antiporters differ in several important respects, and the most physiologically significant of these may be their differences in regulation. The Mg2+-dependent Na+/H+ antiporter controls mitochondrial volume in a dangerous, high-K+ environment. To play this vital role, this porter must always lie poised far from K+/H+ equilibrium; i.e., it must be under dynamic regulation, as proposed in the Mg2+ carrier-brake hypothesis (7). Being regulated, it is not necessary for this antiporter to be cation-selective, since all electroneutral cation movements will be followed by redistributions of anions and water. On the other hand, there is no indication at present that the Mg2+-independent Na+/H+ antiporter is regulated. This transporter is therefore required to exhibit high discrimination against K+ in order to prevent the collapse of matrix volume dueto uncontrolled loss of K+ salts and water (4). Do the properties of the mitochondrial Na+/H+ antiporters help us in any way to understand the plasmalemmal Na+/H+ antiporters? I believe they do, if we allow that there are a limited number of ways in which nature constructs such porters. The difference in cation selectivities very likely reflects a fundamental structural difference between the two mitochondrial antiporters, and this difference appears to be mirrored in two types of plasmalemmal Na+/H+ antiporters. Thus, the Mg2+-independent Na+/H+ antiporter resembles the renal tubular Na+/H+ antiporter in its discrimination against K+ and its competitive inhibition by Li+. On the other hand, the Mg2+-dependent Na+/H+ antiporter resembles a cardiac sarcolemmal Na+/H+ antiporter which transports all alkali cations, including Na+ and K+, and which is inhibited by DCCD and amphiphilic amines (S. Kakar, A. Askari and K. Garlid, in preparation). The existence of the latter class of antiporter in plasmalemma may seem unlikely at first glance, since it would tend to catalyze Na+/K+ exchange and dissipate the effects of the Na+,K+-ATPase. Nevertheless, a sound design principle would be followed if the cell, like mitochondria, were to regulate volume by governing a passive back-flow process rather than an active transport process. In conclusion, it seems premature to conclude that plasma membranes contain only one type of Na+/H+ antiporter. Nor does it seem likely that there is an unlimited variety of such transporters. I propose as a working hypothesis that antiporters from both mitochondria and plasmalemma may be separated into two classes: Na+-selective and non-Na+-selective.(ABSTRACT TRUNCATED AT 400 WORDS)
 ...
PMID:Sodium/proton antiporters in the mitochondrial inner membrane. 285 Jul 31

The central problem for organisms which grow optimally, and in some cases obligately, at pH values of 10 to 11, is the maintenance of a relatively acidified cytoplasm. A key component of the pH homeostatic mechanism is an electrogenic Na+/H+ antiporter which--by virtue of kinetic properties and/or its concentration in the membrane--catalyzes net proton uptake while the organisms extrude protons during respiration. The antiporter is also capable of maintaining a constant pHin during profound elevations in pHout as long as Na+ entry is facilitated by the presence of solutes which are taken up with Na+. Secondary to the problem of acidifying the interior is the adverse effect of the large pH gradient, acid in, on the total pmf of alkalophile cells. For the purposes of solute uptake and motility, the organisms appear to largely bypass the problem of a low pmf by utilizing a sodium motive force for energization. However, ATP synthesis appears not to resolve the energetics problem by using Na+ or by incorporating the proton-translocating ATPase into intracellular organelles. The current data suggest that effective proton pumping carried out by the alkalophile respiratory chain at high pH may deliver at least some portion of the protons to the proton-utilizing catalysts, i.e., the F1F0-ATPase and the Na+/H+ antiporter, by some localized pathway.
 ...
PMID:Bioenergetics of alkalophilic bacteria. 287 Nov 95

The apical transport processes responsible for proton secretion were studied in the isolated perfused rabbit S3 proximal tubule. Intracellular pH (pHi) was measured with the pH dye, 2',7'-bis(carboxyethyl)-5,6-carboxyfluorescein. Steady state pHi in S3 tubules in nominally HCO3(-)-free solutions was 7.08 +/- 0.03. Removal of Na+ (lumen) caused a decrease in pHi of 0.34 +/- 0.06 pH/min. The decrease in pHi was inhibited 62% by 1 mM amiloride (lumen) and was unaffected by 50 microM 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (lumen) and Cl- removal (lumen, bath). After a brief exposure to 20 mM NH4Cl, pHi fell by approximately 0.7 and recovered at a rate of 0.89 +/- 0.15 pH/min in the nominal absence of Na+, HCO3-, organic anions, and SO4(2-) (lumen, bath). 1 mM N,N'-dicyclohexylcarbodiimide (lumen), 1 mM N-ethylmaleimide (lumen), 0.5 mM colchicine (bath), and 0.5 mM iodoacetic acid (lumen, bath) inhibited the Na+-independent pHi recovery rate by 73%, 55%, 77%, and 86%, respectively, whereas 1 mM KCN (lumen, bath) did not inhibit pHi recovery. Reduction of intracellular, but not extracellular chloride, also decreased the Na+-independent pHi recovery rate. In conclusion, the S3 proximal tubule has an apical Na+/H+ antiporter with a Michaelis constant for Na+ of 29 mM and a maximum velocity of 0.47 pH/min. S3 tubules also possess a plasma membrane H+-ATPase that can regulate pHi, has a requirement for intracellular chloride, and utilizes ATP derived primarily from glycolysis.
 ...
PMID:Apical Na+/H+ antiporter and glycolysis-dependent H+-ATPase regulate intracellular pH in the rabbit S3 proximal tubule. 288 87

The ATP synthase (F1F0) of Propionigenium modestum has been purified to a specific ATPase activity of 5.5 units/mg of protein, which is about 6 times higher than that of the bacterial membranes. Analysis by SDS gel electrophoresis indicated that in addition to the five subunits of the F1 ATPase, subunits of Mr 26,000 (a), 23,000 (b), and 7500 (c) have been purified. The ATPase activity of F1F0 was specifically activated about 10-fold by Na+ions. The enzyme was strongly inhibited by dicyclohexylcarbodiimide, venturicidin, tributyltin chloride, and azide. After incubation with [14C]dicyclohexylcarbodiimide, about 3-4 mol of the inhibitor was bound per 500,000 g of the enzyme. The radioactive label was specifically bound to submit c. These subunits form stable aggregates which resist dissociation by SDS at 100 degrees C. The monomer is formed upon heating with SDS to 121 degrees C or by extraction of the membranes with chloroform/methanol. The ATP synthase was incorporated into liposomes by a freeze-thaw-sonication procedure. The reconstituted proteoliposomes catalyzed the transport of Na+ions upon ATP hydrolysis. The transport was completely abolished by dicyclohexylcarbodiimide. Whereas monensin prevented the accumulation of Na+ions, the uptake rate was stimulated 4-5-fold in the presence of valinomycin or carbonyl cyanide m=chlorophenylhydrazone. These results indicate an electrogenic Na+ transport and also that it is a primary event and not accomplished by a H+-translocating ATP synthase in combination with a Na+/H+ antiporter.
 ...
PMID:Characterization of the ATP synthase of Propionigenium modestum as a primary sodium pump. 290 67

Sodium ions were specifically required for citrate degradation by suspensions of K. pneumoniae cells which had been grown anaerobically on citrate. The rate of citrate degradation was considerably lower than the activities of the citrate fermentation enzymes citrate lyase and oxaloacetate decarboxylase, indicating that citrate transport is rate limiting. Uptake of citrate into cells was also Na+ -dependent and was accompanied by its rapid metabolism so that the tricarboxylic acid was not accumulated in the cells to significant levels. The transport could be stimulated less efficiently by LiCl. Li+ ions were cotransported with citrate into the cells. Transport and degradation of citrate were abolished with the uncoupler [4-(trifluoromethoxy)phenylhydrazono]propanedinitrile (CCFP). After releasing outer membrane components and periplasmic binding proteins by cold osmotic shock treatment, citrate degradation became also sensitive towards monensin and valinomycin. The shock procedure had no effect on the rate of citrate degradation indicating that the transport is not dependent on a binding protein. Citrate degradation and transport were independent of Na+ ions in K. pneumoniae grown aerobically on citrate and in E. coli grown anaerobically on citrate plus glucose. An E. coli cit+ clone obtained by transformation of K. pneumoniae genes coding for citrate transport required Na specifically for aerobic growth on citrate indicating that the Na-dependent citrate transport system is operating. Na+ and Li+ were equally effective in stimulating citrate degradation by cell suspensions of E. coli cit+. Citrate transport in membrane vesicles of E. coli cit+ was also Na+ dependent and was energized by the proton motive force (delta micro H+). Dissipation of delta micro H+ or its components delta pH or delta psi by ionophores either totally abolished or greatly inhibited citrate uptake. It is suggested that the systems energizing citrate transport under anaerobic conditions are provided by the outwardly directed cotransport of metabolic endproducts with protons yielding delta pH and by the decarboxylation of oxaloacetate yielding delta pNa+ and delta psi. In citrate-fermenting K. pneumoniae an ATPase which is activated by Na+ was not found. The cells contain however a proton translocating ATPase and a Na+/H+ antiporter in their membrane.
 ...
PMID:Citrate transport in Klebsiella pneumoniae. 294 69


<< Previous 1 2 3 4 5 6 7 8 9 Next >>